Production of lubricating oils



April 23, 1940. F. x. Gow-:Rs

PRODUCTION OF LUBRICATING OILS Filed Sept. 14, 1934 Patented Apr. 23, 1940 )stares PATE OFFICE- PRODUCTION OF LUBRICATING `OILS Application September 14, 1934, Serial No. 743,965

17 Claims.

This invention relates to a lprocess for the production of low cold test, high viscosity oils having loW Conradson carbon and high resistance to oxidation.

It relates more particularly to thekimprovement in low viscosity oils by the removal of relatively W viscosity index constituents and to the improvement; of normally relatively high viscosity index oils by removal of the constituents in tending to or having high Conradson carbon characteristics.

It relates particularly to a process Where such improvement in viscosity index and Conradson carbon is caused by solvent extraction as in the m case of extraction with nitrobenzol. Nitrobenzol was early suggested asa solvent having selective action between relatively high and relatively low viscosity index constituents, and for the `removal of constituents giving oils an undesired high Conradson carbon. While nitrobenzol Was found to be satisfactory in many Ways, it has the great disadvantage, under conditions of elevated temperatures, of acting as an oxidizing, agent, this oxidizing effect resultingin undesired reaction products in the finished oil and equally undesired losses in the solvent used. t

Difficulties are'encountered in the complete removal at times of the nitrobenaol solvent and, in many cases, even by the aid of steam in distillation, under reduced pressure conditions, the nitrobenzol is not completely removed.

Furthermore, When oil is treated with an extraction solvent of the foregoing character, the mixture of oil and solvent separates into a raffinate phase and an extract phase. -The extract phase contains the relatively low viscosity index, or non-paramnic, constituents dissolved in the main body of the extraction solvent, While the raflinate phase contains the relatively highl viscosity index, or paramnic portion, of the oil which is insoluble in the solvent. The raiiinate phase comprises a mixture of this undissolved oil with a portion of the extraction solvent and also retains a portion of the extract phase.

I have found that when the rafnate phase is subjected to distillation for removal of the extraction solvent, the resulting ranate oil retains, and is contaminated by, the concentration of the products that were in the retained portion of the extract phase, the retention'ofthese products affecting adversely the desired characteristics and color of the nished product. c l

Nitrobenzol has many advantages from the standpoint of solvent extraction asv to separation between liquid relatively high and relatively low viscosity index hydrocarbons, but is not satisfactory as a selective solvent as between liquid and solid hydrocarbons, either by itself or as an anti-solvent component of 4a dewaxing mixture. Where 10W cold test, high viscosity oils .5 are required, the dewaxing must be accomplished by solvents other than those containing nitrobenzol, and this necessity calls for the complete removal of the nitrobenzol from the raflinate stage before proceeding with the dewaxing step. 1.0 The removal of the nitrobenzol from the raffinate stage is rather diicult Without causing oxidation of the oils `contained in such stage.

I have discovered that all `of the difficulties heretofore encountered Ain the use of nitrobenzol as a selective solvent, as used in the'improvement of viscosity index of lubricating oils, can be avoided if, instead of removing the nitrobenzol from, the raffinate by distillation, it is removed therefrom by solvent extraction. I have also discovered that it is particularly advantageous if such solvent used for the removal of the nitrobenzol be one suitable for use in the subsequent dewaxing step.

Suitable solvents for this purpose comprise 25 the low-boiling aliphatic ketones, such as acetone and methyl ethyl ketone, since they .have antisolvent properties for Wax. In those instances where the dewaxing step is omitted, other solvents may be used, such as the low-boiling ali- ,30 phatic alcohols containing upto three carbon atoms. For example, ethyl alcohol, or commercial ethyl alcohol, may be used as the Washing solvent. The ketone and alcohol solvents mentioned have boiling points not in excess of about ZOZPF. which is the boiling point of primary propyl alcohol.

I have further discovered that, in the removal of the nitrobenzol solvent from the extract phase,V it is advantageous to do so by means of a solvent having complete solvent action on the nitrobenzol and substantially no solvent action on the extractive matters contained therein.

As an example in the ordinary use of nitrobenzoL4 as a solvent for the improvement of 45 lubricating oils, a Wax-bearing fraction i of a Mid-Continent crude is treated with nitrobenzol by the step countercurrent method at a temperal ture of about 50 F. The raffinate from the nal` step is heated under diminished pressure to re- 50 move the retained nitrobenzol. During this heating, oxidation is quite liable to take place due to the temperatures employed. The extract from` the rst step is likewise subjected to distillation for the recovery of nitrobenzol solvent, and in A55 this step it has also been found that there is a likelihood of considerable oxidation occurring with consequent loss of solvent.

After removal of the nitrobenzol from the ranate, it is dewaxed by any well known means, but most advantageously by means shown in my U. S. Patent No. 1,802,942.

In the improved process, the rainate from the final step is treated in a continuous countercurrent apparatus with approximately two volumes of acetone at a temperature of about 40 F. belowy the miscibility temperature of a mixture of 1 volume of raffinate and 11/2 volumes of acetone. The raffinate coming from this process, and containing acetone, can then be used immediately in the dewaxing step, the dewaxing being accomplished by a mixture of acetone and benzol, or acetone with other modifying solvents, such as toluol, mixtures of benzol and toluol, light petroleum hydrocarbons including light petroleum naphtha, and normally gaseous petroleum fractions of th character of propane and butane.

The acetone extract from the rainate, containing nitrobenzol, dissolved oils of lower viscosity index than the raflinate but higher than the original oil and acetone, has the acetone removed by flash distillation and is returned, to

the extraction system at any desired point Without being exposed to any high degree of heating.

It has been found that the raffinate so treated contains no oxidation products and no trace of nitrobenzol, and is of a noticeably better color, viscosity index and Conradson carbon than is the case of a rafnate having the nitrobenzol removed in the usual manner by distillation; and there has been no breakdown of nitrobenzol in the process.

In order to more fully describe the invention, referencewill now be made to the accompanying ligure, representing a flow diagram for the process when practiced in accordance with the invention as above described.

Ihe wax-bearing oil, which is to beA treated, is conducted from a storage tank I to a mixer 2. It is there mixed with the extraction solvent which, in this case, comprises a mixture of nitrobenzol and dissolved oil forming the extract phase withdrawn from the second stage separating vessel,

to which reference will be made later.

` From the mixer 2, the mixture of oil and nitrobenzol is conducted through a pipe 3 to a first ,stage separating vessel 4. In this separating Ves- The rafnate phase, mixed with some of the nitrobenzol, is withdrawn from the vessel 4,

' wherein it is washed with acetone. The tower I I is arranged for counter-current washing. Accordingly, to facilitate this washing, the rainate is introduced to the lower portion of the tower through the pipe I0, while the acetone is introduced from the Astorage tank l2, through a pipe I3, to the upper portion of the tower I I.

The washed rai-linate from which the nitrobenzol has been removed is withdrawn from the top of tower II, through a pipe I4, to a mixer I5. This washed rainate, already retaining a portion of the acetone wash liquid, is mixed with additional quantities of acetone in the mixer I5. A quantity of benzol is also drawn from the storage tank I 6 and introduced to the mixer I5 for mixing with the washed rainate. The proportions of benzol and acetone are adjusted so as to form with the wax-bearing raffinate a solvent mixture which has selective action between oil and wax at temperatures of the order of 0 F. and below.

'Ihe resulting mixture of oil and solvent is withdrawn from the mixer I5, through a pipe Il, to a chiller I8 wherein it is chilled to a temperature sufciently low to precipitate the wax in solid form.

From the chiller I8, the cold mixture is withdrawn through a pipe I9 to a dewaxing filter 20, wherein the wax is filtered out of the cold liquid mixture. The separated Wax is withdrawn from the filter 20 to a storage tank 2I for such further treatment as may be desired, including recovery of the solvent retained by the wax.

The dewaxed filtrate is withdrawn from the nlter through a pipe 22 to a stripper 23 for the purpose vof removing the solvent from the dewaxed oil. The solvent is removed from the stripper through a condenser 24 for return to the dewaxing system. This solvent, comprising a mixture of acetone and benzol, may be mixed as is with further washedrainate, or, on the other hand, the acetone and benzol may be separated from each other and separately returned to their respective storage tanks I2 and IB, previously mentioned.

The dewaxed oil is withdrawn from the stripper 23, through a pipe 25, to a storage tank 2G,

wherein it is held for further treatment, as will be described later.

Referring again to the washing tower II, the acetone containing dissolved nitrobenzol, removed from the ramnate, is withdrawn from the bottom of the tower Il, through a pipe 2'I, to a still 23. In the still 28, the mixture is subjected to distillation to vaporize and remove the acetone. The vaporized acetone is withdrawn through a condenser 29, and the condensed acetone from there conducted through a pipe 30 to the acetone storage tank I2.

The residue from still 28, comprising nitrobenzol and some oil, is withdrawn through va pipe 3l and conducted to the mixer 2, previously mentioned, wherein it is mixed with fresh incoming wax-bearing oil.

Referring tothe second stage separating vessel 9, the extract phase formed therein and comprising a mixture of oil dissolved in nitrobenzol, is withdrawn through a pipe 32 and conducted to the mixer 2, wherein it is mixed with the fresh incoming charge, as earlier described.

The extract phase formed in the first stage separating vessel 4 is withdrawn therefrom through a pipe 33 and conducted to a still 34. The nitrobenzol is distilled from the Iextract oil in the still 34, Withdrawn through a condenser 35, and the resulting liquid nitrobenzol'returned to the storage tank 1. v

I'he extract oil, remaining in the still 34, is withdrawn to the storage tank 36.

As an example, 1000 gallons of a Mid-Continent wax distillate, having a gravity of 26.3 Baum and a viscosity of seconds at 210 F. and

Conradson carbon of 1.26, isl extracted in a countercurrent step process with 3000 gallons of nitrobenzol at a temperature in the last stage of 50 F. and in the first stage of 65 F. The railinate coming from the final step will contain approximately of nitrobenzol and will amount to approximately 7(55 gallons. This raiiinate is Washed countercurrently with 2000 gallons of acetone, while maintaining a temperature of 40 F., and the washed raiiinate, amounting to approinmately 830 gallons and containing approximately 25% oi acetone, has added to it 696 gallons of acetone and 1651 gallons of benzol, is chilled to -10 F., iiltered to remove the separated solid hydrocarbons, the solvent removed from the nitrate, and the resulting oil steamed to 500 F. in the presence of clay and contact ltered. The resulting oil, amounting to approximately 568 gallons, will have approximately the following characteristics:

Gravity 30 Baume Viscosity at 210 F 67% SayboltUniversal sec. Viscosity index 97 Conradson carbon .08%

Pour test 5 F.

It will 4be of a light yellow color of a decidedly greenish shade, will contain no oxidized oils, and will be comparatively of high resistance to oxidation.

The nitrobenzol extracted. from the rainate layer and containing approximately 13 gallons of dissolved oil will be substantially freed from acetone by distillation, and can be returned to the solvent extraction system.

The original extract may have the nitrobenzol recovered by distillation, or advantageously may have the nitrobenzol removed from the oil by extraction with 95% ethyl alcohol, the alcohol evaporated, and the nitrobenzol returned to the system.

While the example and discussion of the prior art are confined to nitrobenzol, it is for the matter of convenience of illustration only, since other extractive solvents may be used, such as furfural, which, having marked selective action as between differing constituent hydrocarbons, is not especially adapted as a solvent for the production of very low cold test oils. likewise, aniline, while possessing the properties of great selectivity as to bot-h color and removal of undesired compounds, as Well as desirable properties from the standpoint of a component part of a dewaxing mixture, possesses, in the case of highly refined oils, at times, the property of forming addition and substitution products, resulting in certain objectionable color characteristics. Benzaldehyde likewise, while a good selective solvent from all standpoints, has a tendency to cause oil separation when used as a component of a dewaxing mix at very low temperatures, and its removal from the raiiinate in the disclosed` manner, as, for instance, by methyl ethyl ketone, and the use of methyl ethyl ketone as a component part of the subsequent dewaxing mix results in improvement as to colo-r, viscosity and stability of the.

finished oils.

Application of the invention in, connection with selective extraction. solvents broadly has been described in my application Serial No. 743,714 for Solvent reiining of hydrocarbon oil and my application Serial No. 743,715 for Production of lubricating oils, both of which were iiled` September 12, 1934.

Obviously, many modifications and variations of' the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. i v

I claim:

, l. The method of manufacturing oils: of high viscosity index, loW pour point and lo-w Conrad'son carbon content from Wax-bearing fractions o-f a mineral oil which comprises extracting the cil with a relatively high boiling selective extraction solvent, forming an extract phase comprising low viscosity index constituents dissolved in the bulk of the solvent liquid and a raflinate phase comprising high viscosity index constituents and retaining some of the extract phase, separating the two phases, removing the retained extract phase from said raflinate phase by Washing the. raffinate phase with an organic wash solvent boiling at a temperature not in excess of 207 F. and having antisolvent properties for wax, producing a washed oil comprising high viscosity index constituents and some Wash solvent, and dewaxing the high viscosity index constituents in the presence of a chilled solvent mixture having selective action between solid and high viscosity index hydrocarbons and' having as a component part of such chilled solvent mixture the portion of wash solvent retained by the high viscosityindex constituents.

2. The method of manufacturing oils of high viscosity index, low pour point and low Conradson carbon content from Wax-bearing fractions of a mineral oil which comprises extracting the oil with nitrobenzol, forming an extract phase comprising low viscosity index constituents dissolved in the bulk of the solvent liquid and a rainate phase comprising high viscosity index constituents and retaining some of the extract phase, separating the two phases, removing the retained extract phase from said rainate phase by Washing the raiinate phase with an aliphatic ketone selected from the class consisting of acetone and methyl ethyl ketone, producing a washed oil comprising high viscosity index constituents and some wash solvent, and dewaxing the high viscosity index constituents in the presence of a chilled solvent mixture having selective action between solid and high viscosity index hydrocarbons and having as a component part of such chilled solvent mixture the portion of aliphatic ketone wash solvent retained by the high viscosity index constituents.

3. The method oi refining mineral oil which comprises extracting the oil with nitrobenzol, forming an extract phase comprising nitrobenzol and low viscosity index oil dissolved therein, and a raffinate phase comprising high viscosity index oil and a relatively small amount of retained extract phase consisting mainly of nitrobenzol and non-parainic material dissolved in the solvent, separating said extract and rainate phases, and removing the small amount of retained extract phase from the separated raffinate phase by washing the raffinate phase with a substantially nonaqueous organic solvent having substantially complete solvent action on the retained extract phase and substantially no solvent action on the high viscosity index oil.

4. The method according to claim 3 in which the raffinate phase is washed with an organic solvent liquid boiling at a temperature not in excess of about 207 F.

5. The method according to claim 3 in which the raffinate phase is Washed with a low-boiling All aliphatic alcohol containing up to three :"carbon atoms; f

6.' The method according to claim 3 in which the raffinate phase is washed with a low-boiling aliphatic ketone, selected from the class consisting of acetone andl methyl ethyl ketone.

7. The method of refining mineral oil which comprises extracting the oil with a solvent comprising nitrobenzol, forming an extract phase comprising low viscosity index oil dissolved in the bulk of the nitrobenzol and a ralnate phase comprising high viscosityindex oil mixed with a small portion of the nitrobenzol, saidnitrobenzol containing dissolved therein around 2% of relatively non-paraiinic material, separating said extract and raii'inate phases, and removing from the separated raflinate phase both the retained nitrobenzol and small amount of non-paraiinic material dissolved therein by washing said raffinate phase with a relatively low boiling substantially non-aqueous organic wash solvent having substantially complete solvent action on the retained nitrobenzol and the non-parafnic material contained in it and substantially no solvent action on the high viscosity index raffinate oil.

8. A process for separating a liquid hydrocarbon mixture into its components, comprising the steps of extracting said mixture with a high-boiling selective solvent for a component of said mixture, thereby forming liquid ranate and extract phases, separating said liquid phases, and substantially removing the selective solvent from the raiiinate phase by contacting said phase with a polar liquid boiling below about 100 C. which is more miscible with the selective solvent than with the hydrocarbons contained in the said. phase, and chemically inert with respect to said selective solvent under the conditions: of the process, under conditions causing the formation of two liquid phases, separating said second liquid phases, and separately distilling said separated phases to distil off said polar liquid'.

9. The method of rening mineral oil which comprises extracting the oil with a selective extraction solvent, forming an extract phase comprising selective solvent and low viscosity index oil dissolved therein, andI a raffinate phase comprising high viscosity index oil and a relatively small amount of retained extract phase consisting mainly of extraction solvent and non-parainic material dissolved in the solvent, separating said extract and rainate phases, and removing the small amount of retained extract phase from. the separated rainate phase by washing the rainate phase with a substantially non-aqueous, organic solvent having substantially complete solvent action on the retained extract phase and substantially no solvent action on the high viscosity index oil.

10. The process of refining mineral oils which comprises extracting the oil with nitrobenzene, forming a raflnate phase and an extract phase each of which contains nitrobenzene, separating the phases, effecting contact between the railinate phase and a low-boiling alcohol, forming a phase predominantly oil and a phase predominantly solvent, and separating the oil phase from the solvent phase.

11. 'I'he method according to claim 9 in which the raflinate phase is washed with a low-boiling aliphatic alcohol containing up to three carbon atoms.

12. The method according to claim. 9 in which the raflinate phase is washed with ethyl alcohol.

13. The method according to claim 9 in which the raiiinate phase is washed with a low-boiling aliphatic ketone, from the group consisting of acetone and methyl ethyl ketone.

14. The method of rening mineral oil which comprises extracting the oil with furfural, forming an extract phase comprising furfural and low viscosity index oil dissolved therein, and a rainate phase comprising high viscosity index oil and a relatively small amount of retained extract phase consisting mainly of furfural and non-parainic material dissolved in the solvent, separating said extractI and raiinate phases, and removing the small amount of retained extract phase from the separated raflinate phase by washing the rainate phase with a substantially non-aqueous organic solvent having substantially complete solvent action on the retained extract phase and substantially no vsolvent action on the high viscosity index oil.

15. The method according to claim 14 in which the ranate phase is washed with a low-boiling aliphatic alcohol, such as ethyl alcohol.

16. 'I'he method according to claim 14 in which the raflinate phase is washed with a low-boiling aliphatic ketone, such as acetone and methyl ethyl ketone.

17. The method of manufacturing oils of high viscosity index, low pour point and low Conradson carbon content from. wax-bearing fractions of a mineral oil which comprises extracting the oil with a relatively high boiling selective extraction solvent, forming an extract phase comprising loW viscosity index constituents dissolved in the bulk of the solvent liquid and a rafnate phase comprising high viscosity index constituents and retaining some of the extract phase, separating the two phases, removing the retained extract phase from said' rafnate phase by washing the raffinate Iphase with a substantially non-aqueous organic wash solvent having substantially complete solvent action on the retained extract phase and substantially no solvent action on the high viscosity index oil, producing a Washed oil comprising high viscosity index constituents and some wash solvent, and dewaxing the high viscosity index constituents in the presence of a chilled solvent mixture having selective action between solid and high viscosity index hydrocarbons and hav ing as a component part of such chilled solvent mixture the portion of wash solvent retained by the high viscosity index constituents.

FRANCIS X. GOVERS. 

